Rotation of the large scale solar magnetic field has a great importance for the understanding of solar dynamic, for the search of longitidinal structure and for the study of solar-terrestrial relations. 30-year long observations taken at the Wilcox Solar Observatory (USA) in 21-23 cycles have been analysed carefully to deduce magnetic field rotation rate at different latitudes in both hemispheres and its variability in time. The WSO data appear to indicate that additionally to the differential rotation along the latitudes there are running waves of fast rotation of the magnetic field. These torsional waves are running from the poles to the equator with a period of 11 years. The rotation of the magnetic field (RMF) is almost rigid at latitudes above 55 degrees in both hemispheres. The rotation rate in the sub-polar regions is slower when the magnetic field is strong there (during minima of solar activity), and faster when the magnetic field changes polarity (during maxima of solar activity).
The observations of the Sun have been performed over the years, even centuries- Whether are there active longitudes? If yes how stable are they? One of the first The Wilcox Solar Observatory data taken over three cycles N 21, N 22, N 23 have been used to reveal the longitudinal structure of the photospheric magnetic field. Mean over three cycles magnetic field distribution has been calculated in the North and in the South hemispheres as well as at 30 levels of latitude from -75 to 75 degrees. This study was performed using observations of the magnetic field taking into account its polarity or …
A new model has been proposed for magnetic field determination at different distances from the Sun during different solar cycle phases. The model depends on the observed large-scale non-polar photospheric magnetic fields and that measured at polar regions from 55N to 90N and from 55S to 90S,which are the visible manifestations of cyclic changes in the toroidal and poloidal components of the global magnetic field of the Sun. The modeled magnetic field is determined as the superposition of the non-polar and the polar photospheric magnetic field cycle variations. The agreement between the model p…
A statistical study is carried out on the photospheric magnetic nonpotentiality in solar active regions and its relationship with associated flares. We select 2173 photospheric vector magnetograms from 1106 active regions observed by the Solar Magnetic Field Telescope at Huairou Solar Observing Station, National Astronomical Observatories of China, in the period of 1988-2008, which covers most of the 22nd and 23rd solar cycles. We have computed the mean planar magnetic shear angle (\bar{Δϕ}), mean shear angle of the vector magnetic field (\bar{Δψ}), mean absolute vertical current density (\bar…
Large scale solar magnetic field topology has a great influence on the structure of the corona, heliosphera and geomagnetic perturbations. Data obtained over the last three solar cycles have been analysed to reveal the relationships between the photospheric field measured along the line of sight by the WSO group at 30 levels of heliolatitudes from -75 to 75 degrees and the interplanetary magnetic field The main aim of this first paper is to make a direct comparison between the basic structure and dynamics of the photospheric magnetic field and components and intensity of the interplanetary mag…
The evolution of the photospheric magnetic field during the declining phase and minimum of Cycle 23 and the recent rise of Cycle 24 are compared with the behavior during previous cycles. We used longitudinal full-disk magnetograms from the NSO's three magnetographs at Kitt Peak, the Synoptic Optical Long-term Investigations of the Sun (SOLIS) Vector Spectro-Magnetograph (VSM), the Spectromagnetograph and the 512-Channel Magnetograph instruments, and longitudinal full-disk magnetograms from the Mt. Wilson 150-foot tower. We analyzed 37 years of observations from these two observatories that hav…
For groups of photospheric magnetic fields differing in strength the time averaged synoptic maps were obtained on the basis of the National Solar Observatory Kitt Peak data (1976-2003). The latitudinal profiles of magnetic field fluxes were considered separately for each 5 G interval of the field strength B. The changes both of the profile maxima and of the latitudinal localization of these maxima were studied. The obtained results show that the latitudinal distribution of magnetic fields considerably changes at certain values of the field strength: 5 G, 15 G, and 50 G. The magnetic flux for f…
Magnetoacoustic waves in solar magnetic flux tubes may be affected by the presence of background rotational flows. Here, we investigate the behaviour of $m=0$ and $m=\pm 1$ modes of a magnetic flux tube in the presence of linear background rotational flows embedded in a photospheric environment. We show that the inclusion of a background rotational flow is found to have little effect on the obtained eigensolutions for the axisymmetric $m=0$ sausage mode. However, solutions for the kink mode are dependent on the location of the flow resonance modified by the slow frequency. A background rotatio…
Using both wavelet and Fourier analysis, a study has been undertaken of the changes in the quasi-periodic variations in solar photospheric fields in the build-up to one of the deepest solar minima experienced in the past 100 years. This unusual and deep solar minimum occurred between solar cycles 23 and 24. The study, carried out using ground based synoptic magnetograms spanning the period 1975.14 to 2009.86, covered solar cycles 21, 22 and 23. A hemispheric asymmetry in periodicities of the photospheric fields was seen only at latitudes above $\pm45{^{\circ}}$ when the data was divided, based…
The Helioseismic and Magnetic Imager provides 45 s cadence intensity images and 720 s cadence vector magnetograms. These unprecedented high-cadence and high-resolution data give us a unique opportunity to study the change of photospheric flows and sunspot rotations associated with flares. By using the differential affine velocity estimator method and the Fourier local correlation tracking method separately, we calculate velocity and vorticity of photospheric flows in the flaring NOAA AR 11158, and investigate their temporal evolution around the X2.2 flare on 2011 February 15. It is found that …
Distribution of the positive and negative photospheric fields is studied on the base of synoptic maps of the photospheric magnetic field produced by the National Solar Observatory Kitt Peak (NSO Kitt Peak) for 1976-2016. In the analysis only the sign of the field irrespective of its strength is taken into account, emphasizing the role of the fields with average and weak strengths. Time changes in the positive and negative magnetic fields for two hemispheres, for the high latitudes and for the sunspot zone as well as their imbalances are considered. Distributions of fields of opposite polaritie…
Aims. We show how the build-up of magnetic gradients in the Sun's corona may be inferred directly from photospheric velocity data. This enables computation of magnetic connectivity measures such as the squashing factor without recourse to magnetic field extrapolation. Methods.Assuming an ideal evolution in the corona, and an initially uniform magnetic field, the subsequent field line mapping is computed by integrating trajectories of the (time-dependent) horizontal photospheric velocity field. The method is applied to a 12 hour high-resolution sequence of photospheric flows derived from Hinode…
The CoRoT satellite has recently discovered a hot Jupiter that transits across the disc of a F9V star called CoRoT-6 with a period of 8.886 days. We model the photospheric activity of the star and use the maps of the active regions to study stellar differential rotation and the star-planet interaction. We apply a maximum entropy spot model to fit the optical modulation as observed by CoRoT during a uninterrupted interval of about 140 days. Photospheric active regions are assumed to consist of spots and faculae in a fixed proportion with solar-like contrasts. Individual active regions have life…
We study the variability of solar activity using new photospheric proxies originally developed for the analysis of stellar magnetism with the CoRoT and Kepler photometric observations. These proxies are obtained by tracking the temporal modulations in the observations associated to the spots and magnetic features as the Sun rotates. We analyze here 21 years, spanning solar cycles 23 and 24, of the observations collected by the space-based photometric VIRGO and radial velocity GOLF instruments on board the SoHO satellite. The photospheric activity proxy Sph is then calculated for each of the th…
Understanding the characteristics of the solar magnetic field is essential for interpreting solar activities and dynamo. In this research, we investigated the asymmetric distribution of the solar photospheric magnetic field values, using synoptic charts constructed from space-borne high-resolution magnetograms. It is demonstrated that the Lorentzian function describes the distribution of magnetic field values in the synoptic charts much better than the Gaussian function, and this should reflect the gradual decay process from strong to weak magnetic fields. The asymmetry values are calculated u…
We have studied the evolution of magnetic helicity and chirality in an active region over three consecutive solar rotations. The region when it first appeared was named NOAA10923 and in subsequent rotations it was numbered NOAA 10930, 10935 and 10941. We compare the chirality of these regions at photospheric, chromospheric and coronal heights. The observations used for photospheric and chromospheric heights are taken from Solar Vector Magnetograph (SVM) and H_alpha imaging telescope of Udaipur Solar Observatory (USO), respectively. We discuss the chirality of the sunspots and associated H_alph…
We report observations of a steady 20 year decline of solar photospheric fields at latitudes $\geq$45${^{o}}$ starting from $\sim$1995. This prolonged and continuing decline, combined with the fact that Cycle 24 is already past its peak, implies that magnetic fields are likely to continue to decline until $\sim$2020, the expected minimum of the ongoing solar Cycle 24. In addition, interplanetary scintillation (IPS) observations of the inner heliosphere for the period 1983--2013 and in the distance range 0.2--0.8 AU, have also shown a similar and steady decline in solar wind micro-turbulence le…
Long-lived rotational and meridional flows are important ingredients of the solar cycle. Magnetic field images have typically been used to measure these flows on the solar surface by cross-correlating thin longitudinal strips or square patches across sufficiently long time gaps. Here, I use one month of SDO/HMI line-of-sight magnetic field observations, combined with the SWAMIS magnetic feature tracking algorithm to measure the motion of individual features in these magnetograms. By controlling for perturbations due to short-lived flows and due to false motions from feature interactions, I eff…
The variation in area of quiet magnetic network measured over the sunspot cycle should modulate the spatially averaged photospheric temperature gradient, since temperature declines with optical depth more gradually in magnetic flux tube atmospheres. Yet, limb darkening measurements show no dependence upon activity level, even at an rms precision of 0.04%. We study the sensitivity of limb darkening to changes in area filling factor using a 3D MHD model of the magnetized photosphere. The limb darkening change expected from the measured 11 yr area variation lies below the level of measured limb d…
Photospheric magnetic fields were studied using the Kitt Peak synoptic maps for 1976-2003. Only strong magnetic fields (B>100 G) of the equatorial region were taken into account. The north-south asymmetry of the magnetic fluxes was considered as well as the imbalance between positive and negative fluxes. The north-south asymmetry displays a regular alternation of the dominant hemisphere during the solar cycle: the northern hemisphere dominated in the ascending phase, the southern one in the descending phase during Solar Cycles 21-23. The sign of the imbalance did not change during the 11 years…
As one of the most violent eruptions on the Sun, flares are believed to be powered by magnetic reconnection. The fundamental physics involving the release, transfer and deposition of energy have been studied extensively. Taking advantage of the unprecedented resolution provided by the 1.6-m Goode Solar Telescope, here we show a sudden rotation of vector magnetic fields, about 12$^{\circ}$-20$^{\circ}$ counterclockwise, associated with a flare. Unlike the permanent changes reported previously, the azimuth-angle change is transient and co-spatial/temporal with H$α$ emission. The measured azimuth…
The space experiment CoRoT has recently detected a transiting hot Jupiter in orbit around a moderately active F-type main-sequence star (CoRoT-Exo-4a). This planetary system is of particular interest because it has an orbital period of 9.202 days, the second longest one among the transiting planets known to date. We study the surface rotation and the activity of the host star during an uninterrupted sequence of optical observations of 58 days. Our approach is based on a maximum entropy spot modelling technique extensively tested by modelling the variation of the total solar irradiance. It assu…
The structure of electric current and magnetic helicity in the solar corona is closely linked to solar activity over the 11-year cycle, yet is poorly understood. As an alternative to traditional current-free "potential field" extrapolations, we investigate a model for the global coronal magnetic field which is non-potential and time-dependent, following the build-up and transport of magnetic helicity due to flux emergence and large-scale photospheric motions. This helicity concentrates into twisted magnetic flux ropes, which may lose equilibrium and be ejected. Here, we consider how the magnet…
Monitoring chromospheric and photospheric indexes of magnetic activity can provide valuable information, especially the interaction between different parts of the atmosphere and their response to magnetic fields. We extract chromospheric indexes, S and Rhk+, for 59,816 stars from LAMOST spectra in the LAMOST-Kepler program, and photospheric index, Reff, for 5575 stars from Kepler light curves. The log Reff shows positive correlation with log Rhk+. We estimate the power-law indexes between Reff and Rhk+ for F-, G-, and K-type stars, respectively. We also confirm the dependence of both chromosph…
We analyse the topology of photospheric magnetic fields and sub-photospheric flows of several active regions (ARs) that are observed during the peak to descending phase of the solar cycle 23. Our analysis shows clear evidence of hemispheric preferences in all the topological parameters such as the magnetic, current and kinetic helicities, and the 'curl-divergence'. We found that 68\%(67\%) ARs in the northern (southern) hemisphere with negative (positive) magnetic helicities. Same hemispheric preference sign is found for the current helicities in 68\%(68\%) ARs. The hemispheric preferences are…
Solar supergranulation plays an important role in generating and structuring the solar magnetic field and as a mechanism responsible for the 11-year solar cycle. It is clearly detected within SOHO/MDI Dopplergrams, from which a variety of properties may be derived. Techniques that extract spatial, temporal and kinematic characteristics and provide comparisons for the two most recent solar minima are described. Although supergranule lifetimes are comparable between these minima, their sizes maybe slightly smaller during the recent minimum.
Analysis of the structure and dynamics of the magnetic field of the Sun is fundamental for understanding of the origin of solar activity and variability as well as for the study of solar-terrestrial relations. Observations of the large scale magnetic field in the photosphere taken at the Wilcox Solar Observatory from 1976 up to 2007 have been analysed to deduce its latitudinal and longitudinal structures, its differential rotation, and their variability in time. This paper is dedicated to the analysis and dynamics of the latitudinal structure of the solar magnetic field over three solar cycles…
We present an analysis of the starspot evolution, the surface differential rotation (SDR), the correlation between chromospheric activity indicators and the spatial connection between chromospheric and photospheric activities on the active star Kepler-411, using time series photometry over 4 years from Kepler, and spectroscopic data from Keck I 10-m telescope and Lijiang 2.4-m telescope. We constructed the light curve by re-performing photometry and reduction from the Target Pixel Files and Cotrending Basis Vectors with a manually redefined aperture using the software PyKE3. An efficient progr…
Photospheric magnetic fields are studied using synoptic maps from 1976 to 2003 produced at the National Solar Observatory, Kitt Peak (NSO/KP). Synoptic maps were averaged over the time interval of nearly three solar cycles (Solar Cycles 21-23). The change in the latitudinal distribution was considered for the following groups of magnetic field values: B = 0-5 G, B = 5-15 G, B = 15-50 G, and B>50 G. Magnetic fields in each of the above groups have common latitudinal distribution features, while for different field groups these features are significantly different. Each of the groups is closely …
We use daily full-disk vector magnetograms from Vector Spectromagnetograph (VSM) on Synoptic Optical Long-term Investigations of the Sun (SOLIS) system to synthesize the first Carrington maps of the photospheric vector magnetic field. We describe these maps and make a comparison of observed radial field with the radial field estimate from LOS magnetograms. Further, we employ these maps to study the hemispheric pattern of current helicity density, Hc, during the rising phase of the solar cycle 24. Longitudinal average over the 23 consecutive solar rotations shows a clear signature of the hemisp…
Context. Observations of flux emergence indicate that rotational velocities may develop within sunspots. However, the dependence of this rotation on sub-photospheric field strength and twist remains largely unknown. Aims. We investigate the effects of varying the initial field strength and twist of an emerging sub-photospheric magnetic flux tube on the rotation of the sunspots at the photosphere. Methods. We consider a simple model of a stratified domain with a sub-photospheric interior layer and three overlying atmospheric layers. A twisted arched flux tube is inserted in the interior and is …
Sausage waves have been frequently reported in solar magnetic structures such as sunspots, pores, and coronal loops. However, they have not been unambiguously identified in photospheric bright points (BPs). Using high-resolution TiO image sequences obtained with the Goode Solar Telescope at the Big Bear Solar Observatory, we analyzed four isolated BPs. It was found that their area and average intensity oscillate for several cycles in an in-phase fashion. The oscillation periods range from 100 to 200 seconds. We interpreted the phase relation as a signature of sausage waves, particularly slow w…
The line-of-sight (LOS) component of the large-scale photospheric magnetic field has been observed since the 1950s, but the daily full-disk observations of the full vector magnetic field started only in 2010 using the SOLIS Vector Stokes Magnetograph (VSM) and the SDO helioseismic and magnetic imager (HMI). Traditionally, potential field extrapolations are based on the assumption that the magnetic field in the photosphere is approximately radial. The validity of this assumption has not been tested yet. We investigate here the structure and evolution of the three components of the solar large-s…
We discuss the current Standard Solar Model conflict between helioseismology and photospheric abundances, a speculation that connects this anomaly to formation of the gaseous giant planets, and a possible neutrino measurement to directly test solar core metalicity.
Obtaining measurements of chromospheric and photometric activity of stars with near-solar fundamental parameters and rotation periods is important for a better understanding of solar-stellar connection. We select a sample of 2603 stars with near-solar fundamental parameters from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST)-Kepler field and use LAMOST spectra to measure their chromospheric activity and Kepler light curves to measure their photospheric activity (i.e., the amplitude of the photometric variability). While the rotation periods of 1556 of these stars could …
I briefly review the current state of the modelling of photospheric activity based on the high-precision optical light curves obtained with MOST, CoRoT, and Kepler. These models can be used to search for active longitudes where activity is preferentially concentrated, estimate the amplitude of stellar differential rotation, and look for short-term activity cycles as, e.g., in the case of CoRoT-2. In the case of a late-type star accompanied by a transiting hot Jupiter, the small light modulations observed during transits when a dark spot is occulted by the disc of the planet are also briefly co…
We present photometry and spectropolarimetry of the pre-main sequence star HD 106506. A photometric rotational period of ~1.416 +/- 0.133 days has been derived using observations at Mount Kent Observatory (MKO). Spectropolarimetric data taken at the 3.9-m Anglo-Australian Telescope (AAT) were used to derive spot occupancy and magnetic maps of the star through the technique of Zeeman Doppler imaging (ZDI). The resulting brightness maps indicate that HD 106506 displays photospheric spots at all latitudes including a predominant polar spot. Azimuthal and radial magnetic images of this star have b…
Context. The Kepler mission has recently discovered a brown dwarf companion transiting one member of the M4V+M5V visual binary system LHS 6343 AB with an orbital period of 12.71 days. Aims. The particular interest of this transiting system lies in the synchronicity between the transits of the brown dwarf C component and the main modulation observed in the light curve, which is assumed to be caused by rotating starspots on the A component. We model the activity of this star by deriving maps of the active regions that allow us to study stellar rotation and the possible interaction with the brown…
The longitudinal asymmetry of the photospheric magnetic field distribution is studied on the basis of the data of the Kitt Peak National Solar Observatory (synoptic maps for the period 1976 - 2016). The method of vector summing of magnetic fields is used, which allows to decrease the influence of the stochastic components uniformly distributed over the whole longitude interval, and to stress a steady non-axisymmetric component of the field. The distributions of magnetic fields of different intensity are considered separately for the strong (B > 50 G), weak (B < 5 G) and medium (50 > B > 5 G) f…
The High Altitude Water Cherenkov (HAWC) array is sensitive to high energy Cosmic Rays (CR) in the $\sim 10$ to $\sim 200$ TeV energy range, making it possible to construct maps of the so called "Sun Shadow" ($SS$), i. e. of the deficit of CR coming from the direction of the Sun. In this work, we present the variation of the Relative Intensity of the deficit ($SS_{RI}$) for three years of HAWC observations form 2016 to 2018 in which we found a clear decreasing trend of the ($SS_{RI}$) over the studied period, corresponding to the declining phase of the solar cycle 24. By comparing the $SS_{RI}…
We use the synoptic maps of the photospheric magnetic field observed at Wilcox Solar Observatory, Mount Wilson Observatory, Kitt Peak, SOHO/MDI, SOLIS/VSM, and SDO/HMI to study the distribution of weak photospheric magnetic field values in 1974-2018. We fit the histogram distribution of weak field values for each synoptic map of the six data-sets separately with a parametrized Gaussian function in order to calculate the possible shift (to be called here the weak-field asymmetry) of the maximum of the Gaussian distribution from zero. We estimate the statistical significance of the weak-field as…
Properties of the Sun's interior can be determined accurately from helioseismological measurements of solar oscillations. These measurements, however, are in conflict with photospheric elemental abundances derived using 3-D hydrodynamic models of the solar atmosphere. This divergence of theory and helioseismology is known as the $"$solar modeling problem$"$. One possible solution is that the photospheric neon abundance, which is deduced indirectly by combining the coronal Ne/O ratio with the photospheric O abundance, is larger than generally accepted. There is some support for this idea from o…
The present paper discusses results of a statistical study of the characteristics of coronal hole (CH) rotation in order to find connections to the internal rotation of the Sun. The goal is to measure CH rotation rates and study their distribution over latitude and their area sizes. In addition, the CH rotation rates are compared with the solar photospheric and inner layer rotational profiles. We study coronal holes observed within $\pm 60$ latitude and longitude degrees from the solar disc centre during the time span from the 1 January 2013 to 20 April 2015, which includes the extended peak o…
A hemispheric preference in the dominant sign of magnetic helicity has been observed in numerous features in the solar atmosphere: i.e., left-handed/right-handed helicity in the northern/southern hemisphere. The relative importance of different physical processes which may contribute to the observed hemispheric sign preference (HSP) of magnetic helicity is still under debate. Here, we estimate magnetic helicity flux ($dH/dt$) across the photospheric surface for 4,802 samples of 1,105 unique active regions (ARs) that appeared over an 8-year period from 2010 to 2017 during solar cycle 24, using …
We present a new method of visualizing the solar photospheric magnetic field based on the "Magnetic Range of Influence" (MRoI). The MRoI is a simple realization of the magnetic environment in the photosphere, reflecting the distance required to balance the integrated magnetic field contained in any magnetogram pixel. It provides a new perspective on where sub-terrestrial field lines in a Potential Field Source Surface (PFSS) model connect to the photosphere, and thus the source of Earth-directed solar wind (within the limitations of PFSS models), something that is not usually obvious from a re…
The photospheric response to solar flares, also known as coronal back reaction, is often observed as sudden flare-induced changes in vector magnetic field and sunspot motions. However, it remains obscure whether evolving flare ribbons, the flare signature closest to the photosphere, are accompanied by changes in vector magnetic field therein. Here we explore the relationship between the dynamics of flare ribbons in the chromosphere and variations of magnetic fields in the underlying photosphere, using high-resolution off-band H-alpha images and near-infrared vector magnetograms of the M6.5 fla…
Diagnostic techniques for stellar magnetic fields based upon spectropolarimetry. We propose and explore a new technique based upon the linear polarization emitted in Hanle-sensitive lines in disk-integrated stars where a dipolar magnetic field breaks the rotational symmetry of the resonance scattering polarization. A star with a simple dipolar field and a 1-0 spectral line are used to compute polarization amplitudes and angles.Predicted amplitudes are low but within reach of present instruments. A new application of the Hanle effect is proposed and analyzed, a tool that allows measuring of som…
The CoRoT satellite has recently discovered the transits of a telluric planet across the disc of a late-type magnetically active star dubbed CoRoT-7, while a second planet has been detected after filtering out the radial velocity (hereafter RV) variations due to stellar activity. We investigate the magnetic activity of CoRoT-7 and use the results for a better understanding of its impact on stellar RV variations. We derive the longitudinal distribution of active regions on CoRoT-7 from a maximum entropy spot model of the CoRoT light curve. Assuming that each active region consists of dark spots…
The X9.3 flare of September 6, 2017, was the most powerful flare of Solar Cycle 24. It generated strong white-light emission and multiple helioseismic waves (sunquakes). By using data from Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) as well as hard X-ray data from KONUS instrument onboard WIND spacecraft, and Anti-Coincidence System (ACS) onboard the INTERGRAL space observatory, we investigate spatio-temporal dynamics of photospheric emission sources, identify sources of helioseismic waves and compare the flare photospheric dynamics with the hard X-ray (…
Although chromospheric activity cycles have been studied in a larger number of late-type stars for quite some time, very little is known about coronal activity-cycles in other stars and their similarities or dissimilarities with the solar activity cycle. While it is usually assumed that cyclic activity is present only in stars of low to moderate activity, we investigate whether the ultra-fast rotator AB Dor, a K dwarf exhibiting signs of substantial magnetic activity in essentially all wavelength bands, exhibits a X-ray activity cycle in analogy to its photospheric activity cycle of about 17 y…
The correlation between solar irradiance and the 11-year solar activity cycle is evident in the body of measurements made from space, which extend over the past four decades. Models relating variation in solar irradiance to photospheric magnetism have made significant progress in explaining most of the apparent trends in these observations. There are, however, persistent discrepancies between different measurements and models in terms of the absolute radiometry, secular variation and the spectral dependence of the solar cycle variability. We present an overview of solar irradiance measurements…
We reassess the relationship between the photospheric magnetic field strength and the Ca II K intensity for a variety of surface features as a function of the position on the disc and the solar activity level. This relationship can be used to recover the unsigned photospheric magnetic field from images recorded in the core of Ca II K line. We have analysed 131 pairs of high-quality, full-disc, near-co-temporal observations from SDO/HMI and Rome/PSPT spanning half a solar cycle. To analytically describe the observationally-determined relation, we considered three different functions: a power la…
The latitudinal distributions of the yearly mean rotation rates measured respectively by Suzuki in 1998 and 2012 and Pulkkinen $\&$ Tuominen in 1998 are utilized to investigate internal-cycle variation of solar differential rotation. The rotation rate at the solar Equator seems to decrease since cycle 10 onwards. The coefficient $B$ of solar differential rotation, which represents the latitudinal gradient of rotation, is found smaller in the several years after the minimum of a solar cycle than in the several years after the maximum time of the cycle, and it peaks several years after the maxim…
We report here results of spectropolarimetric observations of the ~8Myr classical TTauri star (cTTS) TWHya carried out with ESPaDOnS at the Canada-France-Hawaii Telescope (CFHT) in the framework of the `Magnetic Protostars and Planets' (MaPP) programme, and obtained at 2 different epochs (2008 March and 2010 March). Obvious Zeeman signatures are detected at all times, both in photospheric lines and in accretion-powered emission lines. Significant intrinsic variability and moderate rotational modulation is observed in both photospheric and accretion proxies. Using tomographic imaging, we recons…
